Modern vehicles require fuel management systems that control fuel vapor venting from a vehicle fuel tank to limit fuel filling and that control fuel tank ventilation to prevent overpressure and vacuum conditions in the fuel tank. Fuel filling must be limited to prevent overfilling the fuel tank in order to retain sufficient vapor space above the fuel in the fuel tank to allow vapors to vent to a fuel vapor recovery device during thermal expansion, on-grade parking, and similar conditions.
When refueling a vehicle, a typical pump operator will add a small amount of fuel after an initial fill nozzle shut-off. The operator usually adds this small amount of fuel to “round up” payment to some convenient amount to minimize the amount of change involved in a fuel purchase. Additionally, the operator will often attempt to maximize the amount of fuel pumped into the fuel tank, ostensibly to extend a period of time between fill-ups. To maximize the fuel amount, the operator will dispense the fuel slowly over an extended period of time. Those in the fuel system industry generally describe this as “trickle-fill”.
A control valve made by Alfmeier Corporation, Greenville, S.C., is one part of a comprehensive Onboard Refueling Vapor Recovery (ORVR) vehicle fuel system that allows the pump operator some freedom to “round-up” the fuel tank without overfilling. This control valve is the subject of U.S. patent application Ser. No. 10/727,716, filed Dec. 4, 2003, and serves to vent fuel vapor from the vapor space in a fuel tank during early stages of refueling. The control valve also blocks introduction of fuel in excess of a nominal tank volume to preserve a volume of vapor space in the fuel tank once the fuel tank is filled to its rated capacity.
One drawback with the conventional control valve is that during initial filling and any subsequent trickle filling, liquid fuel forcefully enters the control valve causing splash and carry-over of liquid fuel to the fuel vapor recovery device before the control valve can operate to shut-off fuel filling.
Another drawback of the conventional control valve is a “washing machine” effect that often occurs during a hot, static condition. This condition is schematically illustrated by FIGS. 8a and 8b, which show a typical valve V attached to a fuel tank of a vehicle.
FIG. 8a shows a fuel entry window X defined in a housing Y of the valve V through which liquid fuel enters when the fuel tank is full. FIG. 8b shows the “washing machine” effect occurring when the vehicle is stationary in a hot environment. As the fuel tank expands due to heat, the fuel level drops sufficiently to open a portion of the fuel entry window X. Due to the increased temperature in the tank, pressurized air is forced through this portion of the fuel entry window X and churns the fuel in the housing Y. Turbulence is created in the fuel, which results in air bubbles in the fuel causing the effective density of the fuel to be reduced. The float U, having preset buoyancy, cannot maintain a seal in the less dense, bubble-infused fuel to seal the valve V. This dynamic phenomenon is indicated by a double-arrow D3, which shows the float U “bobbing” up and down, intermittently sealing the valve V, increasing pressure in the tank, intermittently unsealing the valve V, and permitting additional pressurized air into the fuel entry window X. As the liquid fuel is churned up by the turbulence, some liquid fuel undesirably escapes to the fuel vapor recovery device or to atmosphere as indicated by arrow D4.